I did on Saturday, for about 5 seconds.
We had just finished viewing the Rockefeller Center tree with my sister and her kids, and ducked into a store to find a bathroom. I unbuckled Charlie's stroller strap and told him to hold my hand, and held it out. I turned my head for a second to look for the bathroom, but noticed his hand hadn't touched mine yet so I glanced back. He had completely disappeared!
Well he hadn't gone far - he had just gotten distracted by the window display and wandered a few feet away out of my line of sight. I was about 2 seconds from declaring an Amber Alert though! Thankfully I spotted him before the adrenaline flooded my bloodstream...
Learned my lesson... be even more paranoid/vigilant when at the shopping mall with the kids! Or better yet, just never go shopping.
Have you ever lost your LO while shopping?